CARRIER-DENSITY MODULATION EFFECTS IN A TRAVELING-WAVE SEMICONDUCTOR OPTICAL AMPLIFIER - COMMUNICATIONS THEORY ANALYSIS AND EXPERIMENT

A communications theory equivalent model suitable for analyzing carrier-density modulation effects within a traveling-wave semiconductor optical amplifier is derived by linearizing the amplifier rate equation. This model is then used to analyze dual-channel amplification, and it is shown to give results which are in good agreement with those given by both nonlinear polarization theory and experimental measurements. The effect of four-wave mixing on the amplification of many optical channels for worst-case operating conditions is then studied, and it is shown that the individual channels experience different gains. It is also shown that if the individual channel gains are to be confined to lie within a +/- 1-dB band when operating the amplifier at high values of unsaturated power gain, this can be achieved only by using either a channel separation frequency in excess of 5 GHz, or by operating the amplifier 15 dB below saturation.